Field of Invention
The invention relates to a display apparatus and a touch sensing method.
Related Art
Recently, the touch panel has been widely applied to general consumer electronics, such as mobile communication devices, digital cameras, MP3, PDA, GPS, hand-held PC, and even brand-new ultra mobile PC (UMPC). The said touch panel is combined with a display screen to form a touch display device.
In the conventional touch sensing method, first the sensing is implemented along the X-direction and Y-direction, then the touch position along the respective directions can be computed from the magnitude of the signal, and the actual touch coordinates can be obtained by the intersection of the extended lines of the two touch positions along the X-direction and Y-direction. When this method is applied to the situation of limited number of touch sensing lines, the accurate touch coordinates can still be obtained by accurately measuring the magnitude of the signal. However, the accurate measurement also limits the sensing speed.
A known manufacturing method of a touch display apparatus is to directly disposing a touch panel on the display panel of a display module. However, this not only increases the weight and size of the product, but also increases the cost of the touch display apparatus due to the additional touch panel.
Therefore, it is an important subject to provide a display apparatus and a touch sensing method where the touch function can be achieved without additional touch panel so as to make the product lighter and thinner and reduce the cost. Although a couple of solutions have been proposed by adding some sensing elements such as capacitors, resistors or optical devices to the display apparatus, the optical sensing element will influence the display quality for occupying a part of the pixel area and a complicated algorithm is also required to eliminate the interference from the environmental light. Besides, the reliability and durability of the said added elements also need time to verify and the manufacturing process complexity will also be increased.
The major difference between changing the touch sensing matrix from a conventional touch sensor array to a display matrix of a display panel is in the 100˜1000 times reduction in pixel size, for example, from 5 mm×5 mm to 100 μm×300 μm. Therefore, if same detection scheme (detecting the capacitance change caused by the grounding of surface by user body) is used, the base capacitance will become relatively large and thus reduce the signal magnitude. Besides, merging the touch sensing signal with the display driving signal will reduce the time available for sensing and further increase the difficulty of detection. The signal-to-noise ratio can't be improved by connecting multiple electrodes in parallel since connecting multiple electrodes in parallel not only increase the sensing area but also increase the base capacitance. Therefore, the ratio of the sensing capacitance to the basic capacitance can't be changed. This ratio is determined by the display matrix itself.